The present invention relates generally to irrigation control systems and, more particularly, to such systems which may have a mixture of some valves used primarily in lawn irrigation and other valves used primarily in irrigation of shrubs or trees. In the irrigation of lawns, such as on golf courses and the like, the usual requirement is for frequent but relatively light watering. In contrast, irrigation of shrubs and trees generally requires infrequent but relatively deep watering.
Typically, irrigation control systems of the foregoing general type are operable to control a plurality of irrigation valves located at remote points in a golf course, or other property to be irrigated. The control system usually includes a time clock by means of which irrigation can be initiated at any selected hour, or hours, on any selected day, or days, of the week. When irrigation is so initiated, the valve or valves at a first irrigation station are first turned on, and left on for a time determined by a separate station timer. When this time has elapsed, the station-one valves are turned off and the valve or valves associated with a second station are turned on, to be timed by a separate station timer. This process continues until all the station valves have been operated for their preselected times.
In control systems which allow for a mixture of lawn sprinkling valve stations and shrub irrigation stations, the shrub stations are usually the last ones in the sequence, and they may be skipped entirely if the user of the system elects to do so. Thus, the lawn sprinkler stations could be operated, for example, on Monday, Wednesday and Friday, with the shrub stations being operated only on Friday, directly after operation of the lawn stations on that day.
On older control systems, the station timers for each valve station are resistor-capacitor (R-C) timing circuits, but these are inherently unsuitable for measuring relatively long time periods. More modern systems incorporated digital timing circuits which utilize an R-C circuit to provide a basic timing signal, and a digital counter to obtain any desired time interval over a relatively wide range.
Until quite recently, shrubs and trees were irrigated in much the same manner as lawns, i.e., using an aerial spray of water. Now it has become more common practice to irrigate shrubs and trees at ground level by a relatively slow flow of water from a drip irrigator. The optimum times of irrigation for drip irrigation usually exceed the normal times for spray irrigation of shrubs or trees by a factor of four or five. However, irrigation controllers available heretofore which have been capable of providing shrub irrigation can do so only for relatively short times, suitable for spray irrigation. In many applications, however, there is a requirement for a mixture of short-term spray irrigation and long-term drip irrigation of shrubs, and it is highly desirable to be able to selectively assign various shrub irrigation valves as either spray or drip irrigation stations. The present invention is directed to these ends.